Joint design for segmented silicon carbide liner in a fluidized bed reactor

ABSTRACT

Segmented silicon carbide liners for use in a fluidized bed reactor for production of polysilicon-coated granulate material are disclosed, as well as methods of making and using the segmented silicon carbide liners. Non-contaminating bonding materials for joining silicon carbide segments also are disclosed. One or more of the silicon carbide segments may be constructed of reaction-bonded silicon carbide.

FIELD

This disclosure concerns silicon carbide materials, bonding materials,and joint designs for making segmented silicon carbide liners for use ina fluidized bed reactor for making polysilicon-coated granulatematerial.

BACKGROUND

Pyrolytic decomposition of silicon-bearing gas in fluidized beds is anattractive process for producing polysilicon for the photovoltaic andsemiconductor industries due to excellent mass and heat transfer,increased surface for deposition, and continuous production. Comparedwith a Siemens-type reactor, the fluidized bed reactor offersconsiderably higher production rates at a fraction of the energyconsumption. The fluidized bed reactor can be highly automated tosignificantly decrease labor costs.

The manufacture of particulate polycrystalline silicon by a chemicalvapor deposition method involving pyrolysis of a silicon-containingsubstance such as for example silane, disilane or halosilanes such astrichlorosilane or tetrachlorosilane in a fluidized bed reactor is wellknown to a person skilled in the art and exemplified by manypublications including the following patents and publications: U.S. Pat.No. 8,075,692, U.S. Pat. No. 7,029,632, U.S. Pat. No. 5,810,934, U.S.Pat. No. 5,798,137, U.S. Pat. No. 5,139,762, U.S. Pat. No. 5,077,028,U.S. Pat. No. 4,883,687, U.S. Pat. No. 4,868,013, U.S. Pat. No.4,820,587, U.S. Pat. No. 4,416,913, U.S. Pat. No. 4,314,525, U.S. Pat.No. 3,012,862, U.S. Pat. No. 3,012,861, US2010/0215562, US2010/0068116,US2010/0047136, US2010/0044342, US2009/0324479, US2008/0299291,US2009/0004090, US2008/0241046, US2008/0056979, US2008/0220166, US2008/0159942, US2002/0102850, US2002/0086530, and US2002/0081250.

Silicon is deposited on particles in a reactor by decomposition of asilicon-bearing gas selected from the group consisting of silanedisilane (Si₂H₆), higher order silanes (Si_(n)H₂₊₂), dichlorosilane(SiH₂Cl₂), trichlorosilane (SiHCl₃), silicon tetrachloride (SiCl₄),dibromosilane (SiH₂Br₂), tribromosilane (SiHBr₃), silicon tetrabromide(SiBr₄), diiodosilane (SiH₂I₂), triiodosilane (SiHI₃), silicontetraiodide (SiI₄), and mixtures thereof. The silicon-bearing gas may bemixed with one or more halogen-containing gases, defined as any of thegroup consisting of chlorine (Cl₂), hydrogen chloride (HCl), bromine(Br₂), hydrogen bromide (HBr), iodine (I₂), hydrogen iodide (HI), andmixtures thereof. The silicon-bearing gas may also be mixed with one ormore other gases, such as hydrogen (H₂) and/or one or more inert gasesselected from nitrogen (N₂), helium (He), argon (Ar), and neon (Ne). Inparticular embodiments, the silicon-bearing gas is silane, and thesilane is mixed with hydrogen. The silicon-bearing gas, along with anyaccompanying hydrogen, halogen-containing gases and/or inert gases, isintroduced into a fluidized bed reactor and thermally decomposed withinthe reactor to produce silicon which deposits upon seed particles insidethe reactor.

A common problem in fluidized bed reactors is contamination ofsilicon-coated particles in the fluid bed at high operating temperaturesby materials used to construct the reactor and its components. Forexample, nickel has been shown to diffuse into a silicon layer (e.g., ona silicon-coated particle) from the base metal in some nickel alloysused to construct reactor parts. Similar problems arise in fluidized bedreactors configured for pyrolytic decomposition of a germanium-bearinggas to produce germanium-coated particles.

SUMMARY

This disclosure concerns embodiments of silicon carbide materials,bonding materials, and joint designs for making segmented siliconcarbide liners for use in a fluidized bed reactor (FBR) for makingpolysilicon.

Silicon carbide liners for a FBR for production of polysilicon-coatedgranulate material have an inwardly facing surface that at leastpartially defines a reaction chamber. At least a portion of the linermay comprise reaction-bonded SiC, which has, on at least a portion ofthe liner's inwardly facing surface, a surface contamination level ofless than 3% atomic of dopants, and less than 5% atomic of foreignmetals. In one embodiment, the portion has a surface contamination levelof less than 3% atomic of dopants B, Al, Ga, Be, Sc, N, P, As, Ti, andCr, combined. In an independent embodiment, the portion has a surfacecontamination level of less than 1% atomic of phosphorus and less than1% atomic of boron.

In any or all of the above embodiments, the reaction-bonded SiC may havea mobile metal concentration sufficiently low that (i) thepolysilicon-coated granulate material produced in the FBR has a mobilemetal contamination level of ≦1 ppbw, or (ii) a mobile metal partialpressure in the FBR is less than 0.1 Pa during operation of the FBR, or(iii) the mobile metal contamination is ≦1 ppbw and the mobile metalpartial pressure in the FBR is less than 0.1 Pa during operation. Themobile metals may include aluminum, chromium, iron, copper, magnesium,calcium, sodium, nickel, tin, zinc, and molybdenum. In any or all of theabove embodiments, the reaction-bonded SiC may be prepared fromsolar-grade or electronic-grade silicon.

SiC liners for use in an FBR may be constructed from a plurality of SiCsegments bonded together with a bonding material comprising a lithiumsalt. One or more of the segments may comprise reaction-bonded SiC. Thebonding material, before curing, may be an aqueous slurry comprising2500-5000 ppm lithium as lithium silicate and silicon carbide particles.In any or all of the above embodiments, the bonding material may furthercomprise aluminum silicate. In any or all of the above embodiments, thebonding material may have a viscosity from 3.5 Pa·s to 21 Pa·s at 20° C.In any or all of the above embodiments, the bonding material, aftercuring, may comprise 0.4-0.7 wt % lithium as lithium aluminum silicateand 93-97 wt % silicon carbide particles.

A process for constructing a silicon carbide liner from SiC segmentsincludes (i) forming at least one coated edge surface by applying abonding material as disclosed herein to at least a portion of an edgesurface of a first silicon carbide segment; (2) bringing the at least aportion of the edge surface of the first silicon carbide segment intoabutment with at least a portion of an edge surface of a second siliconcarbide segment with at least a portion of the bonding materialpositioned between the abutting edge surfaces of the first siliconcarbide segment and the second silicon carbide segment; and (3) applyingheat to the bonding material, in an atmosphere devoid of hydrocarbons,to form bonded first and second silicon carbide segments. Applying heatmay comprise exposing the abutted first and second silicon carbidesegments to an atmosphere at a first temperature T1 for a first periodof time, increasing the temperature to a temperature T2, and exposingthe abutted first and second silicon carbide segments to the secondtemperature T2, wherein T2>T1, for a second period of time to cure thebonding material. In any or all of the above embodiments, the abuttedSiC segments may be allowed to dry for an initial period of time atambient temperature in air before applying heat.

In any or all of the above embodiments, when two SiC segments are joinedwith the bonding material, one of an edge surface of the first SiCsegment and an adjacent edge surface of the second SiC segment maydefine a female joint portion. The other of the edge surface of thefirst SiC segment and the adjacent edge surface of the second SiCsegment may define a male joint portion cooperatively dimensioned to fitwith the female joint portion. The male joint portion has smallerdimensions than the female joint portion, thereby forming a space whenthe two SiC segments are abutted. The bonding material is disposedwithin the space.

In some embodiments, a segmented SiC liner includes a plurality ofvertically stacked SiC segments. A first SiC segment has an upper edgesurface defining one of an upwardly opening first segment depression oran upwardly extending first segment protrusion. A second SiC segmentlocated above and abutted to the first segment has a lower edge surfacedefining a downwardly opening second segment depression if the firstsegment upper edge surface defines an upwardly extending first segmentprotrusion or a downwardly extending second segment protrusion if thefirst segment upper edge surface defines an upwardly opening firstsegment depression. The protrusion is received within the depression.The protrusion has smaller dimensions than the depression such that thesurface of the depression is spaced apart from the surface of theprotrusion, and a space is located between the depression and theprotrusion. A volume of bonding material is disposed within the space.

Each of the first and second SiC segments may define a tubular wall. Thefirst tubular wall has an annular upper surface, the upper edge surfacebeing at least a portion thereof, and the first segment depression is agroove extending along at least a portion of the upper edge surface orthe first segment protrusion extends upwardly from and along at least aportion of the first segment upper edge surface. The groove or theprotrusion may extend around the entire annular upper surface. Thesecond tubular wall has an annular lower surface, the lower edge surfacebeing at least a portion thereof, and the second segment depression is aprotrusion extending downwardly from and along at least a portion of thelower edge surface or the second segment depression is a groove that isdefined by and extends along at least a portion of the second segmentlower edge surface. The protrusion or depression may extend around theentire annular lower surface. In any or all of these above embodiments,the second SiC segment may include an upper edge surface that defines anupwardly opening second segment depression.

In any or all of the above embodiments, the segmented SiC liner mayinclude one or more additional SiC segments. Each additional SiC segmentmay comprise an upper edge surface defining an upwardly openingdepression and a lower edge surface defining a downwardly extendingprotrusion. The protrusion is received within an upper edge surfacedepression of an adjacent SiC segment located below and abutted to theadditional SiC segment, the protrusion having smaller dimensions thanthe depression of the adjacent SiC segment such that a space is locatedbetween the protrusion and the depression. A volume of the bondingmaterial is disposed within the space.

In any or all of the above embodiments, the segmented SiC liner mayfurther include a terminal SiC segment, which is the uppermost segmentof the liner. In some embodiments, the terminal SiC segment is locatedabove and abutted to the second SiC segment. Alternatively, it may belocated above and abutted to an additional SiC segment, which is locatedabove the second SiC segment. In some embodiments, the terminal SiCsegment has a lower edge surface defining a downwardly extendingterminal segment protrusion received within a depression of a SiCsegment located adjacent to and below the terminal SiC segment, theprotrusion having smaller dimensions than the depression such that aspace is located between the protrusion and the depression. A volume ofthe bonding material is disposed within the space.

In some embodiments, a segmented SiC liner includes a tubular wallcomprising a plurality of laterally joined SiC segments, each laterallyjoined SiC segment having lateral edges and an outer surface that is aportion of the tubular wall outer surface. A volume of bonding materialis disposed between abutting lateral edges of adjacent SiC segments.

In one embodiment, each SiC segment of the tubular wall comprises afirst lateral edge surface defining a laterally opening depression alongat least a portion of the length of the first lateral edge surface, anda second lateral edge surface defining a laterally extending protrusionalong at least a portion of the second lateral edge surface. Theprotrusion has smaller dimensions than the depression such that when afirst lateral edge of a first SiC segment is abutted to a second lateraledge of an adjacent SiC segment, the surface of the depression is spacedapart from the surface of the protrusion and a space is located betweenthe depression and the protrusion. The volume of bonding material isdisposed within the space.

In another embodiment, the tubular wall comprises laterally joinedalternating first and second SiC segments. Each first SiC segmentcomprises a first lateral edge surface defining a laterally openingdepression along at least a portion of the length of the first lateraledge surface. Each second SiC segment comprises a second lateral edgesurface defining a laterally extending protrusion along at least aportion of the length of the second lateral edge surface, the protrusionhaving smaller dimensions than the first lateral edge surface depressionsuch that, when a first lateral edge of the first segment is abutted tothe second lateral edge. The protrusion has smaller dimensions than thedepression such that, when the first lateral edge of the first segmentis abutted to the second lateral edge, the surface of the first segmentdepression is spaced apart from the surface of the second segmentprotrusion and a space is located between the first segment depressionand the second segment protrusion, and the volume of bonding material isdisposed within the space.

A segmented SiC liner may comprise vertically stacked first and secondtubular walls, each tubular wall comprising a plurality of laterallyjoined SiC segments as described above. A volume of bonding material isdisposed between adjacent laterally joined SiC segments of each tubularwall. Additionally, a volume of bonding material is disposed between thefirst and second tubular walls. In such embodiments, each SiC segment ofthe first tubular wall further comprises an upper edge surface definingan upwardly opening first tubular wall segment depression. Each SiCsegment of the second tubular wall further comprises a lower edgesurface defining a downwardly extending second tubular wall segmentprotrusion received within the first tubular wall segment depression.The second tubular wall segment protrusion has smaller dimensions thanthe first tubular wall segment depression, such that a space is locatedbetween the protrusion and the depression when the first and secondtubular wall segments are abutted.

In some of the above embodiments, each second tubular wall segmentfurther comprises an upper edge surface that defines an upwardly openingdepression. In such embodiments, the segmented SiC liner may furthercomprise one or more additional tubular walls, each additional tubularwall comprising a plurality of laterally joined additional SiC segments.Each additional SiC segment comprises a first lateral edge defining alaterally opening depression along at least a portion of its length, asecond lateral edge defining a laterally extending protrusion along atleast a portion of its length, an upper edge surface defining anupwardly opening depression, and a lower edge surface defining adownwardly extending protrusion.

In any or all of the above embodiments, the segmented SiC liner mayfurther comprise a terminal tubular wall comprising a plurality oflaterally joined terminal SiC segments. Each terminal SiC segmentcomprises a first lateral edge defining a laterally opening depressionalong at least a portion of its length, a second lateral edge defining alaterally extending protrusion along at least a portion of its length,and a lower edge surface defining a downwardly extending protrusionreceived in an upwardly opening depression of a tubular wall segmentlocated below the terminal SiC segment.

In any or all of the above embodiments, at least one retaining membermay extend around the cylindrical outer surface of each tubular wallcomprising a plurality of laterally joined SiC segments. The retainingmember may have a linear coefficient of thermal expansion similar toSiC, such as a linear coefficient of thermal expansion ranging from2×10⁻⁶/K to 6×10⁻⁶/K. In some embodiments, the retaining member isconstructed of molybdenum or a molybdenum alloy.

A fluidized bed reactor for production of polysilicon-coated granulatematerial comprises a vessel having an outer wall, and a silicon carbideliner as disclosed herein, the liner being positioned outwardly of theouter wall such that the inner surface of the liner defines a portion ofa reaction chamber. The SiC liner may be at least partially constructedof reaction-bonded SiC. The SiC liner may be constructed from SiCsegments. In any or all of the above embodiments, the FBR may furthercomprise at least one heater positioned between the outer wall and thesegmented silicon carbide liner, at least one inlet having an openingpositioned to admit a primary gas comprising a silicon-bearing gas intothe reaction chamber, a plurality of fluidization gas inlets, whereineach fluidization gas inlet has an outlet opening into the reactionchamber, and at least one outlet for removing silicon-coated productparticles from the vessel.

The foregoing and other features and advantages of the invention willbecome more apparent from the following detailed description, whichproceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional elevational view of a fluidizedbed reactor.

FIG. 2 is a schematic oblique view of a segmented liner including pluralstacked segments.

FIG. 3 is a schematic partial cross-sectional view, taken along line 3-3of FIG. 2, showing the boundary between two vertically abutted siliconcarbide segments.

FIG. 4 is a schematic exploded view of a first silicon carbide segmentand a second silicon carbide segment of the segmented liner of FIG. 2.

FIG. 5 is a schematic cross-sectional view, taken along line 5-5 of FIG.2, of a portion of a segmented liner illustrating three verticallyabutted silicon carbide segments.

FIG. 6 is a schematic elevational view of a terminal silicon carbidesegment.

FIG. 7 is a schematic oblique view of a segmented liner including plurallaterally joined segments.

FIG. 8 is a schematic oblique view of one segment of a liner thatincludes plural laterally joined segments.

FIG. 9 is schematic partial cross-sectional view, taken along line 9-9of FIG.7, showing the boundary between two laterally abutted siliconcarbide segments.

FIG. 10 is a schematic oblique view of a segmented liner includingplural vertically abutted segments, each comprised of laterally abuttedsegments and encompassing retaining elements.

FIG. 11 is a schematic oblique view of a segmented liner includingplural stacked tubular wall segments, each tubular wall segmentincluding plural laterally abutted segments.

FIG. 12 is a schematic exploded view of portions of two abutting stackedwall segments.

FIG. 13 is a schematic oblique view of one segment of the terminaltubular wall segment of FIG. 11

FIG. 14 is a schematic oblique view of the segmented liner of FIG. 11,wherein a plurality of retaining elements surrounds the verticallyjoined tubular wall segments.

DETAILED DESCRIPTION

This disclosure concerns embodiments of silicon carbide materials,bonding materials, and joint designs for making segmented siliconcarbide liners for use in a fluidized bed reactor for makingpolysilicon. A fluidized bed reactor (FBR) for making granularpolysilicon may include an inwardly-facing liner in the reactionchamber. The liner prevents polysilicon granule contamination arisingfrom reactor components positioned outside the liner. The liner isconstructed of a non-contaminating material, such as silicon carbide.

However, manufacturing and reactor design limitations may not allow fora single-piece silicon carbide liner to be prepared. For example, it maynot be possible to make a sufficiently large, single-piece siliconcarbide liner for a commercial-scale FBR. Accordingly, a silicon carbideliner may be assembled from a plurality of silicon carbide segments. Aneed exists for joint designs and bonding materials suitable forconstructing segmented silicon carbide liners. Additionally, the siliconcarbide purity is a consideration. For example, some silicon carbidesare prepared using boron nitride additives, which produce undesirableboron contamination of polysilicon granules under reaction conditionswithin the FBR.

I. DEFINITIONS AND ABBREVIATIONS

The following explanations of terms and abbreviations are provided tobetter describe the present disclosure and to guide those of ordinaryskill in the art in the practice of the present disclosure. As usedherein, “comprising” means “including” and the singular forms “a” or“an” or “the” include plural references unless the context clearlydictates otherwise. The term “or” refers to a single element of statedalternative elements or a combination of two or more elements, unlessthe context clearly indicates otherwise.

Unless explained otherwise, all technical and scientific terms usedherein have the same meaning as commonly understood to one of ordinaryskill in the art to which this disclosure belongs. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present disclosure, suitable methods andmaterials are described below. The materials, methods, and examples areillustrative only and not intended to be limiting. Other features of thedisclosure are apparent from the following detailed description and theclaims.

Unless otherwise indicated, all numbers expressing quantities ofcomponents, percentages, temperatures, times, and so forth, as used inthe specification or claims are to be understood as being modified bythe term “about.” Accordingly, unless otherwise indicated, implicitly orexplicitly, the numerical parameters set forth are approximations thatmay depend on the desired properties sought, limits of detection understandard test conditions/methods, or both. When directly and explicitlydistinguishing embodiments from discussed prior art, the embodimentnumbers are not approximates unless the word “about” is recited.

Unless otherwise indicated, all percentages referring to a compositionor material are understood to be a percent by weight, i.e., % (w/w). Forexample, a composition comprising 2% lithium includes 2 g lithium per100 g of the composition. Where expressly noted, percentages referringto a substance may be atomic percentages, i.e., the number of atoms per100 atoms. For example, a substance comprising 1% atomic phosphorusincludes one phosphorus atom per one hundred atoms in the substance.Similarly, concentrations expressed as parts per million (ppm) or partsper billion (ppb) are understood to be in terms of weight unlessotherwise indicated, e.g., 1 ppm=1 mg/kg. Where expressly noted,concentrations may be expressed as ppma (ppm atomic) or ppba, e.g., 1ppma=1 atom in 1,000,000 atoms. In order to facilitate review of thevarious embodiments of the disclosure, the following explanations ofspecific terms are provided:

Acceptor: An atom capable of accepting an electron (p-type dopants),thus generating holes in the valence band of silicon atoms; acceptorsinclude Group III elements, such as B, Al, Ga, also Be, Sc.

Atomic percent: The percent of atoms in a substance, i.e., the number ofatoms of a particular element per 100 atoms of the substance.

Donor: An atom capable of donating an electron to serve as a chargecarrier in the silicon carbide (n-type dopants); the remaining fourelectrons coordinate with silicon; donors include Group V elements, suchas N, P, As; also Ti, Cr, Sb.

Dopant: An impurity introduced into a substance to modulate itsproperties; acceptor and donor elements replace elements in the crystallattice of a material, e.g., a semiconductor.

Electronic-grade silicon: Electronic-grade, or semiconductor-grade,silicon has a purity of at least 99.99999 wt %, such as a purity from99.9999-99.9999999 wt % silicon. The percent purity may not includecertain contaminants, such as carbon and oxygen. Electronic-gradesilicon typically includes ≦0.3 ppba B, ≦0.3 ppba P, ≦0.5 ppma C, <50ppba bulk metals (e.g., Ti, Cr, Fe, Ni, Cu, Zn, Mo, Na, K, Ca), ≦20 ppbwsurface metals, ≦8 ppbw Cr, ≦8 ppbw Ni, ≦8 ppba Na. In some instances,electronic-grade silicon includes ≦0.15 ppba B, ≦0.15 ppba P, ≦0.4 ppmaC, ≦10 ppbw bulk metals, ≦0.8 ppbw surface metals, ≦0.2 ppbw Cr, ≦0.2ppbw Ni, ≦0.2 ppba Na.

Foreign metal: As used herein, the term “foreign metal” refers to anymetal present in silicon carbide, other than silicon.

LCTE: Linear coefficient of thermal expansion, a measure of thefractional change in length of a material per degree of temperaturechange.

Mobile metal: As used herein, the term “mobile metal” refers to a metalatom or metal ion that may migrate out of a substance (e.g., out ofsilicon carbide) or vaporize at operating conditions of a fluidized bedreactor and contribute to product contamination. Mobile metals includeGroup IA metals, Group IIA metals, Group IIIA metals, transition metals,and cations thereof.

Reaction-bonded silicon carbide (RBSiC): Reaction-bonded silicon carbidemay be produced by reacting porous carbon or graphite with moltensilicon. Alternatively, RBSiC may be formed by exposing a finely dividedmixture of silicon carbide and carbon particles to liquid or vaporizedsilicon at high temperatures whereby the silicon reacts with the carbonto form additional silicon carbide, which bonds the original siliconcarbide particles together. RBSiC often contains a molar excess ofunreacted silicon, which fills spaces between silicon carbide particles,and may be referred to as “siliconized silicon carbide.” In someprocesses, a plasticizer may be used during the manufacturing processand subsequently burned off.

Solar-grade silicon: Silicon having a purity of at least 99.999 wt %atomic. Furthermore, solar-grade silicon typically has specifiedconcentrations of elements that affect solar performance. According toSemiconductor Equipment and Materials International (SEMI) standardPV017-0611, solar-grade silicon may be designated as grade I-IV. Forexample, Grade IV solar-grade silicon contains <1000 ppba acceptors (B,Al), <720 ppba donors (P, As, Sb), <100 ppma carbon, <200 ppbatransition metals (Ti, Cr, Fe, Ni, Cu, Zn, Mo), and <4000 ppba alkaliand earth alkali metals (Na, K, Ca). Grade I solar-grade siliconcontains <1 ppba acceptors, <1 ppba donors, <0.3 ppma C, <10 ppbatransition metals, and <10 ppba alkali and earth alkali metals.

Surface contamination: Surface contamination refers to contamination(i.e., undesired elements, ions, or compounds) within surface layers ofa material, such as a silicon carbide segment. Surface layers includethe outermost atomic or molecular layer of the material as well asatomic/molecular layers extending inwardly to a depth of 25 μm in thematerial. Surface contamination may be determined by any suitable methodincluding, but not limited to, scanning electron microscopy, energydispersive x-ray spectroscopy, or secondary ion mass spectrometry.

II. FLUIDIZED BED REACTOR

FIG. 1 is a simplified schematic diagram of a fluidized bed reactor 10for producing silicon-coated particles. The reactor 10 extends generallyvertically, has an outer wall 20, a central axis A₁, and may havecross-sectional dimensions that are different at different elevations.The reactor shown in FIG. 1 has five regions, I-V, of differingcross-sectional dimensions at various elevations. The reaction chambermay be defined by walls of different cross-sectional dimensions, whichmay cause the upward flow of gas through the reactor to be at differentvelocities at different elevations.

Silicon-coated particles are grown by pyrolytic decomposition of asilicon-bearing gas within a reactor chamber 30 and deposition ofsilicon onto particles within a fluidized bed. One or more inlet tubes40 are provided to admit a primary gas, e.g., a silicon-bearing gas or amixture of silicon-bearing gas, hydrogen and/or an inert gas (e.g.,helium, argon) into the reactor chamber 30. The reactor 10 furtherincludes one or more fluidization gas inlet tubes 50. Additionalhydrogen and/or inert gas can be delivered into the reactor throughfluidization inlet tube(s) 50 to provide sufficient gas flow to fluidizethe particles within the reactor bed. At the outset of production andduring normal operations, seed particles are introduced into reactor 10through a seed inlet tube 60. Silicon-coated particles are harvested byremoval from reactor 10 through one or more product outlet tubes 70. Aliner 80 may extend vertically through the reactor 10. In somearrangements, the liner is concentric with the reactor wall 20. Theillustrated liner 80 is generally a circular cylinder in shape, i.e., atubular liner. In some embodiments, a probe assembly 90 extends into thereactor chamber 30. The reactor 10 further includes one or more heaters.In some embodiments, the reactor includes a circular array of heaters100 located concentrically around reactor chamber 30 between liner 80and outer wall 20. In some systems, a plurality of radiant heaters 100is utilized with the heaters 100 spaced equidistant from one another.

The temperature in the reactor differs in various portions of thereactor. For example, when operating with silane as thesilicon-containing compound from which silicon is to be released in themanufacture of polysilicon particles, the temperature in region I, i.e.,the bottom zone, is ambient temperature to 100° C. (FIG. 1). In regionII, i.e., the cooling zone, the temperature typically ranges from50-700° C. In region III, the intermediate zone, the temperature issubstantially the same as in region IV. The central portion of regionIV, i.e., the reaction and splash zone, is maintained at 620-760° C.,and advantageously at 660-690° C., with the temperature increasing to700-900° C. near the walls of region IV, i.e., the radiant zone. Theupper portion of region V, i.e., the quench zone, has a temperature of400-450° C.

Polysilicon-coated granulate particles are produced by flowing asilicon-containing gas through the fluidized bed reactor containing aseed particle within the reactor chamber under conditions sufficient toeffect pyrolysis of the silicon-containing gas and deposition of apolycrystalline silicon layer on the seed particle to form apolysilicon-coated particle.

Surfaces in contact with seed particles and/or silicon-coated particlesin reactor chamber 30 can be a source of product contamination. Softmetals, for example, are prone to galling from contact with fluidizedsilicon-coated particles. The term “galling” refers to wear and transferof material between metallic surfaces that are in direct contact withrelative movement. Silicon-coated particles can be contaminated by thetransferred metal. Galling also causes wear and tear of metalcomponents, leading to reactor downtime as components are replaced orthe metal surfaces are ground or machined to return them to conditionfor reuse. Thus, there is a need for improved reactor surfaces that willbetter withstand reactor conditions, reduce product contamination, orboth.

A non-contaminating liner has an inwardly facing surface that at leastpartially defines the reaction chamber and reduces productcontamination. The liner prevents polysilicon-coated granulecontamination arising from reactor components positioned outside theliner. Suitable liner materials include, but are not limited tonon-contaminating silicon carbides. Silicon carbide liners, however, canpresent challenges when working with commercial-scale fluidized bedreactors (FBRs). For example, manufacturing and/or reactor designlimitations may preclude using a single-piece SiC liner. Accordingly, aSiC liner may be constructed of segments that are joined to form theliner.

The SiC liner extends through at least a portion of region IV, i.e., thereaction and splash zone, of the FBR. Advantageously, the liner extendsthrough the length of region IV. The liner may further extend throughregions I, II, III, V, or any combination thereof. In some examples, theliner extends through at least a portion of region II, region III,region IV, and at least a portion of region V as shown in FIG. 1.

III. SILICON CARBIDE LINERS

Silicon carbide liners for fluidized bed reactors advantageously areconstructed from SiC that does not cause significant productcontamination when the SiC liner is exposed to operating conditions ofthe FBR. In some embodiments, at least a portion of the liner isconstructed from reaction-bonded SiC (RBSiC).

In some embodiments, an inwardly facing surface of the portion of theliner comprising RBSiC has surface contamination levels of less than 3%atomic of dopants and less than 5% atomic of foreign metals. Dopants inRBSiC include B, Al, Ga, Be, Sc, N, P, As, Ti, Cr, or any combinationthereof. In some embodiments, the portion has a surface contaminationlevel of less than 3% atomic of dopants B, Al, Ga, Be, Sc, N, P, As, Ti,and Cr, combined. The inwardly facing surface of the liner portionconstructed of RBSiC advantageously has a surface contamination levelcomprising less than 1% atomic of phosphorus and less than 1% atomic ofboron.

The RBSiC desirably has a mobile metal concentration sufficiently lowthat the polysilicon-coated granulate material produced in the fluidizedbed reactor has a mobile metal contamination level of ≦1 ppbw asmeasured by inductively coupled plasma mass spectroscopy (ICPMS) andbased on the entire mass of the granule. For aluminum, a contaminationlevel of 1 ppbw or greater might result when aluminum is present in theRBSiC at a sufficient concentration that an aluminum partial pressure inthe FBR is at least 1 Pa, e.g., at least 1 Pa at operating conditionswithin the FBR. For heavier elements (e.g., Fe, Cr), undesirable productcontamination levels may occur at lower partial pressures. In someembodiments, the RBSiC has a mobile metal concentration sufficiently lowthat a total mobile metal partial pressure in the FBR is less than 0.1Pa for the sum of all mobile metal partial pressures during operation ofthe FBR. The mobile metals include aluminum, chromium, iron, copper,magnesium, calcium, sodium, nickel, tin, zinc, and molybdenum. Partialpressure is calculated based on the contamination level measured byICPMS in the granulate material. Vapor pressures of metals can beestimated by the Antoine equation:

log p(atm)=A+B×T ⁻¹ +C×log(T)+D×T×10⁻³,

where p is metal vapor pressure (atm), T is temperature in Kelvins, A,B, C, and D are component-specific constants (Alcock, ThermochemicalProcesses Principles and Models, Butterworth-Heinemann, 2001, p. 38).The calculation assumes that all the vapors of the particular impurityare incorporated into the granulate material. The impurity vapors may beassumed to obey the ideal gas law. Moles or mass of the impurity in thereactor is calculated with the ideal gas law. A concentration in thegranulate material is then calculated using the total mass of granulatematerial in the FBR.

In some embodiments, the RBSiC is siliconized SiC produced by exposing afinely divided mixture of silicon carbide and carbon particles to liquidor vaporized silicon at high temperatures. In certain embodiments, theliquid or vaporized silicon is solar-grade or electronic-grade silicon.

IV. SEGMENTED LINERS

A. Vertically Stacked Segments

A segmented silicon carbide liner 80 for use in a fluidized bed reactorfor production of polysilicon-coated granulate material may comprise afirst SiC segment 82, a second SiC segment 84 stacked on top of thefirst segment 82, and a volume of bonding material 110 disposed betweenabutting edge surfaces of the first and second SiC segments (FIGS. 2 and3). The first, or lower, SiC segment 82, also referred to as aninitiator segment, has a first segment upper edge surface 82 b definingan upwardly opening first segment depression 82 c. In some embodiments,the first SiC segment has a lower edge surface that is flat (i.e., thelower edge surface does not include a depression or a protrusion),thereby facilitating a gas-tight seal when the liner 80 is inserted intothe fluidized bed reactor chamber. The second SiC segment 84 is locatedabove and abutted to the first SiC segment 82. The second SiC segment 84has a second segment lower edge surface 84 d defining a downwardlyextending second segment protrusion 84 e received within the firstsegment depression 82 c. The first segment depression 82 c and secondsegment protrusion 84 e are female and male joint portions,respectively. In some examples, the joint portions have atongue-and-groove configuration, wherein the first segment depression 82c corresponds to the groove and the second segment protrusion 84 ecorresponds to the tongue.

The second segment protrusion 84 e has smaller dimensions than the firstsegment depression such that, when the protrusion 84 e is received inthe depression 82 c, the surface of the first segment depression isspaced apart from the surface of the second segment protrusion and aspace is located between the second segment protrusion 84 e and thefirst segment depression 82 c. The space has a suitable size toaccommodate a volume of bonding material. Although the bonding materialcan bond the first SiC segment to the second SiC segment in the absenceof a space, the space facilitates even distribution of the bondingmaterial and allows excess bonding material to flow out and be removedas pressure is applied to the SiC segments. In the absence of a spacebetween the depression and protrusion, the bonding material may notdistribute evenly, creating high and low points. A high area of bondingmaterial with a small contact area creates an area of high pressure orstress as the SiC segments are brought into abutment, which may causethe SiC segment(s) to break. In some examples, the space has a heighth₁, measured vertically, of 0.2-0.8 mm, such as a height of 0.4-0.6 mm.The bonding material 110 is disposed within the space between the secondsegment protrusion 84 e and the first segment depression 82 c. In someembodiments, the bonding material comprises 0.4-0.7 wt % lithium aslithium aluminum silicate and silicon carbide as described infra. Thebonding material may further comprise aluminum silicate.

A person of ordinary skill in the art understands that, in an alternatearrangement, the protrusion may extend upward from the lower segment andthe depression may be located on the lower edge surface of the uppersegment, i.e., the first segment upper edge surface 82 b may define anupwardly extending first segment protrusion 82 c and the second segmentlower edge surface 84 d may define a downwardly opening depression 84 e.However, the arrangement illustrated in FIG. 3 is more convenient forretaining the uncured bonding material, which may be a slurry or apaste.

In some examples, the first SiC segment 82 comprises a first tubularwall 82 a having an annular upper surface 82 b (FIG. 4). The firstsegment upper edge surface 82 b is at least a portion of the annularupper surface, and the first segment depression 82 c is a groove that isdefined by and extends along at least a portion of the first segmentupper edge surface 82 b. In some embodiments, the depression 82 cextends as a ring around the entire annular upper surface. The secondSiC segment 84 comprises a first tubular wall 84 a having an annularlower surface 84 d (FIG. 4). The second segment lower edge surface 84 dis at least a portion of the annular lower surface, and the secondsegment protrusion 84 e extends downwardly from and along at least aportion of the second segment lower edge surface 84 d. In someembodiments, the protrusion 84 e extends as a ring around the entireannular lower surface 84 d.

In some embodiments, the segmented silicon carbide liner comprises oneor more additional silicon carbide segments. In the example shown inFIG. 2, the liner 80 comprises three silicon carbide segments 82, 84,86. Each of the segments may have a tubular, or substantiallycylindrical, configuration. In some arrangements, each of the segmentshas the same cross-sectional area, forming a vertical cylinder whenstacked. However, it is not required that all of the segments haveidentical cross-sectional areas. Instead, the segments may vary incross-sectional area such that the segmented liner may have differentdiameters at different heights. A person of ordinary skill in the artunderstands that the segmented liner may include two, three, four, ormore than four segments. The number of SiC segments is determined, atleast in part, by the desired height of the liner and the height of theindividual segments. Manufacturing limitations may determine the heightof individual SiC segments.

As shown in FIG. 5, a SiC segment 84 positioned between two adjacent SiCsegments 82, 86 has an upper edge surface 84 b defining an upwardlyopening segment depression 84 c and a lower edge surface 84 d defining adownwardly extending segment protrusion 84 e. The protrusion 84 e isreceived within an upper edge surface depression 82 c defined by anupper edge surface 82 b of an adjacent SiC segment 82 located below andabutted to the SiC segment 84. The protrusion 84 e has smallerdimensions than the depression 82 c of the adjacent silicon carbidesegment 82 such that the surface of the adjacent silicon carbide segmentdepression 82 c is spaced apart from the surface of the protrusion 84 eand a space is located between the protrusion 84 e and the depression 82c of the adjacent silicon carbide segment 82. A volume of bondingmaterial 110 is disposed within the space. Similarly the depression 84 creceives a protrusion 86 e defined by a lower edge surface 86 d of anadjacent SiC segment 86 located above and abutted to the SiC segment 84.The protrusion 86 e has smaller dimensions than the depression 84 c suchthat the surface of the depression 84 c is spaced apart from the surfaceof the protrusion 86 e and a space is located between the protrusion 86e and the depression 84 c. A volume of bonding material 110 is disposedwithin the space.

In some embodiments, a segmented SiC liner comprises a plurality ofvertically stacked SiC segments alternating between segments havingprotrusions on both of the upper and lower edge surfaces and segmentshaving depressions on both of the upper and lower edge surfaces.

In some examples, a segmented SiC liner 80 includes an uppermost orterminal SiC segment, e.g., segment 86 of FIG. 2 that has a tongue orgroove only on the downwardly facing annular surface. FIGS. 5 and 6 showa top terminal segment 86 that has a terminal segment lower edge surface86 d defining a downwardly extending terminal segment protrusion 86 e.The terminal segment protrusion 86 e is received within an adjacentsegment depression, e.g., second segment depression 84 c, and hassmaller dimensions than the adjacent segment depression such that thesurface of the adjacent segment depression is spaced apart from thesurface of the terminal segment protrusion 86 e and a space is locatedbetween the terminal segment protrusion 86 e and the adjacent segmentdepression. A volume of bonding material 110 is disposed within thespace. The terminal SiC segment 86 need not have an upper edge surfacedefining a depression or protrusion; instead the upper edge surface maybe substantially planar as shown in FIG. 2. Although FIGS. 2 and 5illustrate terminal SiC segment 86 abutted to second SiC segment 84, aperson of ordinary skill in the art understands that one or moreadditional SiC segments may be stacked in layers between segments 84 and86. Advantageously, each additional segment has a configurationsubstantially similar to segment 84 with an upwardly opening segmentdepression defined by its upper edge surface and a downwardly extendingsegment protrusion defined by its lower edge surface. Terminal SiCsegment 86 is located above, abutted to, and rests on the adjacent SiCsegment immediately below it.

In some embodiments, one or more of the silicon carbide segments isformed from reaction-bonded SiC, as described supra, that has a surfacecontamination level of less than 1% atomic of boron and less than 1%atomic of phosphorus. The RBSiC may be substantially devoid of boron andphosphorus. As used herein, “substantially devoid” means that that theRBSiC includes a total of less than 2% atomic of boron and phosphorus,such as a total of less than 1% atomic B and P. Advantageously, theRBSiC also has a mobile metal concentration sufficiently low to providea mobile metal partial pressure less than 1×10⁻⁶ atmospheres at anoperating temperature range of the fluidized bed reactor.

B. Laterally Joined Segments

A segmented SiC liner 200 for use in a fluidized bed reactor forproduction of polysilicon-coated granulate material may include at leastone tubular wall 210 having an annular outer surface and comprising aplurality of laterally joined SiC segments 212, 214, 216, 218, 220 (FIG.7). A volume of bonding material is disposed between abutting lateraledge surfaces of each pair of adjacent SiC segments.

The representative liner 200 illustrated in FIG. 7 comprises a tubularwall 210 that includes laterally joined SiC segments 212, 214, 216, 218,220, each segment having lateral edges and an outer surface that definesa portion of the outer surface of the tubular wall 210. A person ofordinary skill in the art, however, understands that the liner mayinclude more or fewer laterally joined SiC segments. It may bepreferable to use fewer segments to reduce contamination from bondingmaterial used to join the segments. However, the number of segments alsomay be determined in part by handling ease when assembling the liner.

As shown in FIG. 8, each SiC segment, e.g., exemplary segment 212,comprises (i) an outer surface 212 a defining a portion of the annularouter surface of the tubular wall 210, (ii) a first lateral edge surface212 f defining a laterally opening depression 212 g along at least aportion of the length of the first lateral edge surface 212 f, and (iii)a second lateral edge surface 212 h defining a laterally extendingprotrusion 212 i along at least a portion of the length of the secondlateral edge surface 212 h. In some embodiments, the depression 212 gand protrusion 212 i extend along the entire length of the first lateraledge surface 212 f and second lateral edge surface 212 i, respectively.The depression 212 g and the protrusion 212 i are female and male jointportions, respectively. In some examples, the joint portions have atongue-and-groove configuration, wherein the depression 212 gcorresponds to the groove and the protrusion 212 i corresponds to thetongue. In some embodiments, each SiC segment has a lower edge surfacethat is flat (i.e., the lower edge surface does not include a depressionor a protrusion), thereby facilitating a gas-tight seal when the lineris inserted into the fluidized bed reactor chamber.

The second lateral edge protrusion 212 i of each segment has smalleredge dimensions than the first lateral edge surface depression 212 g ofeach segment. Accordingly, with reference to FIG. 9, when a firstlateral edge 212 f of a first SiC segment 212 is abutted to a secondlateral edge 214 h of an adjacent SiC segment 214, the surface of thefirst segment depression 212 g is spaced apart from the surface of theadjacent segment protrusion 214 i and a space is located between thefirst segment depression 212 g and the adjacent segment protrusion 214i. A volume of bonding material 205 is disposed within the space betweenthe first segment depression 212 g and the adjacent segment protrusion214 i. In some examples, the space has a width w₂, measuredhorizontally, of 0.2-0.8 mm, such as a width of 0.4-0.6 mm. The bondingmaterial 205 is disposed within the space between the first segmentdepression 212 g and the second segment protrusion 214 i. In someembodiments, the bonding material comprises 0.4-0.7 wt % lithium aslithium aluminum silicate and silicon carbide as described infra. Thebonding material may further comprise aluminum silicate.

In some embodiments, a segmented SiC liner comprises a plurality ofalternating SiC segments having laterally opening depressions on bothlateral edge surfaces and SiC segments having laterally extendingprotrusions on both lateral edge surfaces. In other words, segment 212,for example, may have a first lateral edge 212 f defining a laterallyopening depression 212 g and a second lateral edge 212 h defining alaterally opening depression 212 i. Alternate segments, e.g., segment214, may have a first lateral edge 214 f defining a laterally extendingprotrusion 212 g and a second lateral edge 214 h defining a laterallyextending protrusion 214 i.

One or more of the silicon carbide segments may be formed fromreaction-bonded SiC, as described supra, that has a surfacecontamination level of less than 1% atomic of boron and less than 1%atomic of phosphorus. In some embodiments, the RBSiC is substantiallydevoid of boron and phosphorus. Advantageously, the RBSiC also has amobile metal concentration sufficiently low to provide a mobile metalpartial pressure less than 1×10⁻⁶ atmospheres at an operatingtemperature range of the fluidized bed reactor.

In some embodiments, at least one retaining member 230 extends aroundthe annular outer surface of the tubular wall 210 (FIG. 10). As shown inFIG. 10, a plurality of retaining members 230 may extend around theannular outer surface of tubular wall 210. Desirably, the retainingmember 230 is constructed of a material having a linear coefficient ofthermal expansion (LCTE) substantially similar to the LCTE of siliconcarbide. If the LCTE values of the retaining member and the SiC aresignificantly different, the retaining member and SiC will havedifferent magnitudes of expansion under operating conditions of thefluidized bed reactor, thereby potentially rendering the retainingmember ineffective or fracturing the SiC. The LCTE of SiC is3.9-4.0×10⁻⁶/K. In some examples, the retaining member is constructed ofa material having a LCTE ranging from 2×10⁻⁶/K to 6×10⁻⁶/K, such as aLCTE ranging from 3×10⁻⁶/K to 5×10⁻⁶/K or from 3.5×10⁻⁶/K 5×10⁻⁶/K.Suitable materials for the retaining member include, but are not limitedto, molybdenum (LCTE=4.9×10⁻⁶/K) and certain molybdenum alloys (e.g.,TZM molybdenum—99.2-99.5 wt % Mo, 0.5 wt % Ti, and 0.08 wt % Zr).

C. Laterally and Vertically Joined Segments

As illustrated in FIG. 11, a segmented SiC liner 300 for use in afluidized bed reactor for production of polysilicon-coated granulatematerial may include (i) a first tubular wall 310, also referred to asan initiator wall, having a cylindrical outer surface and comprising aplurality of laterally joined SiC segments (e.g., segments 311, 312,313), each segment having lateral edges and an outer surface that is aportion of the outer surface of tubular wall 310; (ii) a second tubularwall 320 located above and abutted to the first tubular wall 310, thesecond tubular wall 320 having a cylindrical outer surface andcomprising a plurality of laterally adjacent SiC segments (e.g.,segments 321, 322, 323), each segment having lateral edges and an outersurface that is a portion of the outer surface of tubular wall 320;(iii) a volume of the bonding material (not shown) disposed between eachpair of adjacent laterally joined SiC segments of the first tubular wall310; (iv) a volume of the bonding material (not shown) disposed betweeneach pair of adjacent laterally joined SiC segments of the secondtubular wall 320; and (v) volume of bonding material comprising alithium salt, the bonding material (not shown) disposed between thefirst and second tubular walls 310, 320.

The representative liner 300 illustrated in FIG. 11 includes sixlaterally joined SiC segments in each tubular wall. For example, tubularwall 330 includes SiC segments 331-336. A person of ordinary skill inthe art, however, understands that each tubular wall layer may comprisemore or fewer SiC segments. The segments of each tubular wall layer maybe positioned such that the lateral edges of each SiC segment arelaterally staggered relative to the lateral edges of SiC segmentsvertically adjacent to the segment. For example, lateral edges 322 f,322 h of segment 332 are laterally spaced apart from lateral edges ofsegments 312, 313 below and segments 332, 333 above. A staggeredarrangement advantageously provides additional mechanical strength tothe liner 300.

With reference to FIGS. 11 and 12, in some embodiments, each SiCsegment, such as exemplary segment 312, of the first tubular wall 310comprises (i) an outer surface 312 a defining a portion of the annularouter surface of the tubular wall 310, (ii) a first tubular wall segmentupper edge surface 312 b defining an upwardly opening first tubular wallsegment depression 312 c, (iii) a first lateral edge surface 312 fdefining a laterally opening depression (not shown) along at least aportion of the length of the first lateral edge surface 312 f, and (iv)a second lateral edge surface 312 h defining a laterally extendingprotrusion 312 i along at least a portion of the length of the secondlateral edge surface 312 h, the protrusion 312 i having smallerdimensions than the first lateral edge surface depression. In someembodiments, each SiC segment of the first tubular wall 310 has a loweredge surface that is flat (i.e., the lower edge surface does not includea depression or a protrusion), thereby facilitating a gas-tight sealwhen the liner is inserted into the fluidized bed reactor chamber.

Each SiC segment, such as exemplary segment 322, of the second tubularwall 320 comprises (i) an outer surface 322 a defining a portion of theannular outer surface of the tubular wall 320, (ii) a first lateral edgesurface 322 f defining a laterally opening depression 322 g along atleast a portion of the length of the first lateral edge surface 322 f,(iii) a second lateral edge surface 322 h defining a laterally extendingprotrusion (not shown) along at least a portion of the length of thesecond lateral edge surface 322 h, the protrusion having smallerdimensions than the first lateral edge surface depression 312 g, and(iv) second tubular wall segment lower edge surface 322 d defining adownwardly extending second tubular wall segment protrusion 322 ereceived within the first tubular wall segment depression 312 c andhaving smaller dimensions than the first tubular wall segment depression312 c. When the first tubular wall segment upper edge surface 312 b andthe second tubular wall segment lower edge surface 322 d are verticallyabutted, the surface of the first tubular wall segment depression 312 cis spaced apart from the surface of the second tubular wall segmentprotrusion 322 e and a space is located between the second tubular wallsegment protrusion 322 e and the tubular wall first segment depression312 c. The volume of bonding material disposed between the first andsecond tubular walls 310, 320 is disposed within the space between thesecond tubular wall segment protrusion 322 e and the tubular wall firstsegment depression 312 c.

In some examples, the segmented SiC liner 300 further comprises at leastone retaining member 340 extending around the annular outer surface ofthe first tubular wall 310, and at least one retaining member 340extending around the annular outer surface of the second tubular wall320 (FIG. 13). As illustrated in FIG. 13, the segmented SiC liner 300may include a plurality of retaining members 340 extending around eachof the first tubular wall and the second tubular wall.

In some embodiments, each segment of the second tubular wall 320, suchas exemplary segment 322, further comprises an upper edge surface 322 bthat defines an upwardly opening second tubular wall segment depression322 c (FIG. 11).

The segmented SiC liner 300 may further comprise a terminal tubular wall330 located above and abutted to the second tubular wall 320 (FIGS. 10,13). The terminal tubular wall 330 comprises a plurality of laterallyjoined terminal SiC segments (e.g., segments 332, 334, 336). As shown inFIG. 13, each terminal SiC segment, such as exemplary segment 332,comprises (i) a first lateral segment edge surface 332 f defining alaterally opening depression 332 g along at least a portion of thelength of the first lateral segment edge surface 332 f, (ii) a secondlateral segment edge surface 332 h defining a laterally extendingprotrusion 332 i along at least a portion of the length of the secondsegment lateral edge surface 332 h, the protrusion 332 i having smallerdimensions than the first segment lateral edge surface depression 332 g,and (iii) a segment lower edge surface 332 d defining a downwardlyextending terminal tubular wall segment protrusion 332 e received withinthe second tubular wall segment depression 322 c and having smallerdimensions than the second tubular wall segment depression 322 c. Whenthe terminal tubular wall segment lower edge surface 332 d and thesecond tubular wall segment upper edge surface 322 b are verticallyabutted, the surface of the second tubular wall segment depression 322 cis spaced apart from the surface of the terminal tubular wall segmentprotrusion 332 e and a space is located between the terminal tubularwall segment protrusion 332 e and the second tubular wall segmentdepression 322 c. A volume of bonding material comprising a lithium saltis disposed within the space between the terminal tubular wall segmentprotrusion 332 e and the second tubular wall segment depression 322 c.

In some embodiments, the segmented silicon carbide liner includes one ormore additional layers of tubular walls. In the example shown in FIG.11, the liner 300 comprises three tubular walls 310, 320, 330, eachtubular wall comprising a plurality of laterally joined SiC segments,e.g., 312, 314, 316, 322, 324, 326, 332, 334, 336. A person of ordinaryskill in the art understands that the segmented liner may include two,three, four, or more than four tubular walls, each tubular wallcomprising a plurality of SiC segments. The number of tubular walls isdetermined, at least in part, by the desired height of the liner and theheight of the individual tubular walls. Manufacturing limitations maydetermine the height of individual SiC segments laterally joined to formthe individual tubular walls.

Each additional tubular wall advantageously will have a configurationsubstantially similar to tubular 320 of FIG. 11. Each additional tubularwall has an annular outer surface and comprises a plurality of laterallyjoined additional silicon carbide segments. As illustrated in FIG. 12for representative SiC segment 322, each additional SiC segmentcomprises (i) an outer surface 322 a defining a portion of the annularouter surface of the tubular wall 320, (ii) an upper edge surface 322 bthat defines an upwardly opening depression 322 c, (iii) a lower edgesurface 322 d defining a downwardly extending protrusion 322 e (ii) afirst lateral edge surface 322 f defining a laterally opening depression322 g along at least a portion of the length of the first lateral edgesurface 322 f, and (iv) a second lateral edge surface 322 h defining alaterally extending protrusion 322 i along at least a portion of thelength of the second lateral edge surface 322 h, the protrusion 322 ihaving smaller dimensions than the first lateral edge surface depression312 g.

V. BONDING MATERIALS

Suitable bonding materials for joining silicon carbide segments (i)provide a joint having sufficient mechanical strength to withstandoperating conditions (e.g., vibrational stresses) within a fluidized bedreactor, (ii) are thermally stable at operating temperatures within theFBR when cured, (iii) provide a joint that is at least moderately leaktight for gases, and (iv) do not produce undesirable levels of productcontamination. A curable bonding material comprising a lithium salt mayprovide the desired characteristics.

In some embodiments, the uncured bonding material comprises 2500-5000ppm lithium, such as from 3000-4000 ppm lithium. In some embodiments,the lithium salt is lithium silicate.

The uncured bonding material may be an aqueous slurry or pastecomprising lithium silicate. The bonding material may further comprise afiller material. Desirably, the filler material does not producesignificant contamination of the product during FBR operation.Advantageously, the filler material has a thermal coefficient ofexpansion similar to silicon carbide to reduce or eliminate separationof the bonding material from the SiC surfaces when heated. Suitablefiller materials include silicon carbide particles.

The bonding material may also include a thickening agent to provide adesired viscosity. The bonding material advantageously has a spreadableconsistency with sufficient viscosity to minimize undesirable running ordripping from coated surfaces. in some embodiments, the bonding materialhas a viscosity from 3.5 Pa·s to 21 Pa·s at 20° C., such as a viscosityfrom 5-20 Pa·s, 5-15 Pa·s, or 10-15 Pa·s at 20° C. In some examples, thebonding material includes aluminum silicate powder as a thickeningagent. Aluminum silicate is stable at FBR operating temperatures and isnot easily reduced by hydrogen. Thus, aluminum silicate is a suitable,non-contaminating thickening agent. In certain embodiments, the bondingmaterial has a suitable viscosity when the aluminum silicate is presentin a sufficient concentration to provide 700-2000 ppm aluminum, such asfrom 1000-1500 ppm aluminum.

When cured, the bonding material may comprise lithium aluminum silicateand silicon carbide, such as 0.4-07 wt % lithium and 93-97 wt % siliconcarbide. In some embodiments, the cured bonding material has sufficientstrength to provide joints that can withstand a mass load of at least 5kg.

In some examples, the bonding material is an aqueous slurry comprising2500-5000 ppm lithium as lithium silicate, 700-2000 ppm aluminum asaluminum silicate, and silicon carbide particles. The slurry has aviscosity from 3.5 Pa·s to 21 Pa·s at 20° C. In certain embodiments, thebonding material is an aqueous slurry comprising 3000-4000 ppm lithiumas lithium silicate, 1000-1500 ppm aluminum as aluminum silicate, andsilicon carbide powders.

Advantageously, the cured bonding material does not release deleteriousquantities of contaminants when exposed to operating conditions withinthe FBR. In particular, the bonding material does not releasesignificant quantities of boron, phosphorus, or aluminum during FBRoperation. Advantageously, the cured bonding material does not releasethermally unstable compounds of Group I-VI elements or transition metalsduring FBR operation. In some embodiments, the uncured bonding materialcomprises <50 ppm P, <40 ppm P, or <30 ppm P, and <10 ppm B, <5 ppm B,or <1 ppm B.

In some embodiments, the cured bonding material comprises 0.4-0.7 wt %lithium, primarily as lithium aluminum silicate, and silicon carbide. Insome embodiments, the cured bonding material comprises 0.4-0.6 wt %lithium, primarily as lithium aluminum silicate, and silicon carbide. Insome examples, the cured bonding material comprises 0.4-0.6 wt %lithium, primarily as lithium silicate, and 93-97 wt % silicon carbide.The cured bonding material may further include lithium aluminumsilicate, aluminum silicate, cristobalite (SiO₂), or a combinationthereof. In some examples, the cured bonding material comprises 1.8-2.4wt % lithium aluminum silicate, 2.0-2.5 wt % aluminum silicate, and0.4-0.8 wt % cristobalite. In certain examples, the cured bondingmaterial included 0.5 wt % lithium as determined by the x-raydiffraction pattern of the cured phase and by using the standardreference intensity ratio (RIR) phase quantification method (R. Jenkinsand R. L. Snyder, Introduction to X-Ray Powder Diffractometry, JohnWiley & Sons, Inc., 1996, p. 374). In one embodiment, the cured bondingmaterial contained 0.5 wt % lithium as lithium aluminum silicate, 95 wt% silicon carbide, 2.1 wt % lithium aluminum silicate, 2.3 wt % aluminumsilicate, and 0.6 wt % cristobalite.

VI. PREPARATION OF SEGMENTED SILICON CARBIDE LINERS

Two silicon carbide segments are joined by applying a bonding materialas disclosed herein to at least a portion of an edge surface of a firstsilicon carbide segment to form a coated edge surface. At least aportion of the edge surface of the first silicon carbide segment isbrought into abutment with at least a portion of an edge surface of asecond silicon carbide segment with at least a portion of the bondingmaterial positioned between the abutting edge surfaces of the firstsilicon carbide segment and the second silicon carbide segment. Heat isthen applied to the bonding material to form bonded first and secondsilicon carbide segments. Heating may be performed in an atmospheresubstantially devoid of hydrocarbons, e.g., in air or nitrogen.Embodiments of the disclosed bonding material form a sufficient bondafter heating without the requirement of a cooling step.

In some examples, bonding material is applied to at least a portion ofan edge surface of the first SiC segment and at least a portion of anedge surface of the second SiC segment. The bonding material is appliedto the edge surface(s) by any suitable process including spreading,squeezing, wiping, or brushing the bonding material onto the edgesurface(s). In some examples, the bonding material is applied using aspatula, a syringe, or a squeezable bag with an aperture or attachednozzle. After bringing the edge surfaces of the first and second SiCsegments into abutment, excess bonding material is removed, such as bywiping, before heating the SiC segments to cure the bonding material.Advantageously, the abutted edges of the first and second SiC segmentsdefine male and female joint portions (e.g., a protrusion and adepression) cooperatively dimensioned to provide a space between themale and female joint portions when the edges are abutted, wherein thebonding material is disposed within the space.

Applying heat to the bonding material may include two or more heatingsteps. In some embodiments, applying heat comprises exposing the bondingmaterial to an atmosphere at a first temperature T1 for a first periodof time, increasing the temperature to a second temperature T2, whereinT2>T1, and exposing the bonding material to the second temperature T2for a second period of time to cure the bonding material. Heating isperformed in an atmosphere substantially devoid of hydrocarbons, such asin air or in a nitrogen atmosphere. Heat may be applied to the bondingmaterial, or to the bonding material and the abutted first and secondSiC segments. Heating both the bonding material and the abutted SiCsegments advantageously minimizes differences in material expansion andcontraction during heating and cooling, thereby reducing likelihood ofcracking or separation of the components.

The first temperature T1 and first period of time are sufficient tovaporize water from the bonding material. The first temperature T1desirably is sufficiently low to avoid boiling the water or cracking thebonding material as it dries. In some examples, T1 is within the rangeof 90-110° C., such as within the range of 90-100° C. or 90-95° C. Thefirst period of time is at least one hour, such as at least two hours or2-4 hours. The temperature is gradually increased from ambienttemperature to T1 and then maintained at T1 for the first period oftime. The temperature may be increased at a rate of 1-4° C./minute, suchas a rate of 2-3° C./minute. In some instances, the temperature wasincreased from ambient temperature to 93-94° C. at a rate of 2-3°C./minute, and maintained at 93-94° C. for 2 hours under nitrogen flow.

The second temperature T2 is within the range of 250-350° C., such aswithin the range of 250-300° C., 250-275° C. or 255-265° C. The secondperiod of time is at least one hour, such as at least two hours or 2-4hours. The temperature is gradually increased from T1 to T2, and thenmaintained at T2 for the second period of time. The temperature may beincreased at a rate of 3-8° C./minute, such as a rate of 5-6° C./minute.In some instances, the temperature was increased from T1 to 260° C. at arate of 5-6° C./minute and maintained at 260° C. for 2 hours undernitrogen flow.

Optionally, the joined SiC segments may be further heated from thesecond temperature T2 to a third temperature T3 and maintained at T3 fora third period of time. The temperature T3 is be within the range of350-450° C., such as within the range of 350-400° C., 360-380° C. or370-375° C. The third period of time is at least one hour, such as atleast two hours or 2-4 hours. The temperature is gradually increasedfrom T1 to T2, and then maintained at T2 for the second period of time.The temperature may be increased at a rate of 7-10° C./minute, such as arate of 8-9° C./minute.

In some embodiments, the abutted first and second SiC segments areallowed to dry for an initial period of time at ambient temperaturebefore applying heat. In some examples, an initial period of drying isperformed in air at ambient temperature. The initial period of dryingmay be performed in sunlight. Without wishing to be bound by anyparticular theory of operation, an initial period of drying in ambienttemperature, such as at ambient temperature in sunlight, facilitatesslow diffusion of solvent (e.g., water) from the bonding materialwithout leaving air pockets or defects within the joint and providesadditional contact time between the bonding material and the SiCsurfaces. The bond between the bonding material and the SiC surface maybe strengthened by SiC surface roughness or alkali attack of lithiumions on free silicon on the SiC surface when the SiC is reaction-bondedSiC, which includes free silicon between the SiC particles. When thefree silicon is exposed to lithium ions in an air atmosphere, Si—Osurface species are created. During subsequent curing (at temperaturesT2 and, optionally, T3), the Si—O bond reacts with silicates in thebonding material to form a three-dimensional silica network between theabutted SiC segments.

VII. EXAMPLES Example 1 Evaluation of Bonding Materials

Potassium silicate and lithium silicate-based bonding materials arecommercially available, e.g., Ceramabond 890-K and 890-L, where K and Lrefer to potassium and lithium, respectively (Aremco Products, Inc.,Valley Cottage, N.Y.). Both bonding materials included fine siliconcarbide particles as fillers and aluminum silicate as a thickeningagent. The bonding materials were available as pre-mixed slurries.

Each bonding material was mixed thoroughly before use by shaking for 5minutes or stirring with a mechanical stirrer. Silicon carbide jointsurfaces were cleaned with a metal brush and wiped clean with a cleancloth. Bonding material was applied to matching male and female joints(i.e., tongue-and-groove joints) using a spatula. Excess bondingmaterial was wiped off. Typically, three pairs of silicon carbidesegments (5-8 cm in length) were tested per set of conditions to ensurerepeatability. The male and female joints were pressed and clampedtogether. The clamped joints were dried for 2 hours at room temperature.In some cases, the clamped joints were dried in sunlight for 2 hours.

The joints subsequently were placed into a muffle furnace. Thetemperature was ramped from room temperature to 93° C. at a rate of 2.8°C./minute and maintained at 93° C. for 2 hours under nitrogen flow. Thetemperature then was increased from 93° C. to 260° C. at a rate of 5.6°C./minute, and maintained at 260° C. for 2 hours under nitrogen flow.When the bonding material included potassium silicate (Ceramabond 890-K,the temperature subsequently was increased from 260° C. to 371° C. at arate of 8.3° C./minute, and maintained at 371° C. for 2 hours undernitrogen flow.

A simple lever arm rig was used for comparing the joint strength of thecured, bonded SiC segments in a repeatable manner. One SiC segment of ajoined pair was held in a clamp. A mass was hung from the other SiCsegment of the joined pair. Masses up to 5 kg were used. For eachmeasurement, the lever arm distance (distance between the hang point forthe mass at the joint) was kept constant for all measurements.

Both bonding materials formed joints that easily withstood a 5-kg massload. Attempts to break each joint by hand demonstrated that jointsformed with the lithium silicate-based bonding material could be brokenwith a moderate-to-strong force. The joints formed with the potassiumsilicate-based joints could not be broken by hand.

Although the potassium silicate-based bonding material was stronger,thermodynamic equilibrium calculations predicted that potassium wouldvaporize and contaminate the silicon product during fluidized bedreactor operation. Similar calculations for the lithium silicate-basedbonding material predicted that the binder would be stable under theconditions with the fluidized bed reactor and would not vaporize to anysignificant degree. Tests completed in a fluidized bed reactor confirmedthe predictions. Although potassium contamination occurred with thepotassium silicate-based bonding material, no significant lithium levelwas detected in the silicon product when the lithium silicate-basedbonding material was used.

X-ray diffraction analysis was performed for the cured potassiumsilicate-based bonding material. The XRD analysis showed a mixture ofsilicon carbide polymorphs 4H and 6H. Minor amounts of twoaluminosilicate phases and cristobalite (SiO₂, tetragonal) were alsodetected.

In view of the many possible embodiments to which the principles of thedisclosed invention may be applied, it should be recognized that theillustrated embodiments are only preferred examples of the invention andshould not be taken as limiting the scope of the invention. Rather, thescope of the invention is defined by the following claims. We thereforeclaim as our invention all that comes within the scope and spirit ofthese claims.

We claim:
 1. A segmented silicon carbide liner for a fluidized bed reactor for production of polysilicon-coated granulate material, comprising: a first silicon carbide segment having a first segment upper edge surface defining one of an upwardly opening first segment depression or an upwardly extending first segment protrusion; a second silicon carbide segment located above and abutted to the first silicon carbide segment, the second silicon carbide segment having a second segment lower edge surface defining a downwardly opening second segment depression if the first segment upper edge surface defines an upwardly extending first segment protrusion or a downwardly extending second segment protrusion if the first segment upper edge surface defines an upwardly opening first segment depression, the protrusion being received within the depression and having smaller dimensions than the depression such that the surface of the depression is spaced apart from the surface of the protrusion and a space is located between the protrusion and the depression; and a volume of bonding material comprising a lithium salt, the bonding material disposed within the space between the protrusion and the depression.
 2. The segmented silicon carbide liner of claim 1, wherein: the first silicon carbide segment comprises a first tubular wall having an annular upper surface, the first segment upper edge surface being at least a portion of the annular upper surface, and the first segment depression is a groove that is defined by and extends along at least a portion of the first segment upper edge surface or the first segment protrusion extends upwardly from and along at least a portion of the first segment upper edge surface; and the second silicon carbide segment comprises a second tubular wall having an annular lower surface, the second segment lower edge surface being at least a portion of the annular lower surface, and the second segment protrusion extends downwardly from and along at least a portion of the second segment second edge surface or the second segment depression is a groove that is defined by and extends along at least a portion of the second segment lower edge surface.
 3. The segmented silicon carbide liner of claim 2, wherein the first segment depression extends around the entire first segment annular upper surface or the first segment protrusion extends around the entire first segment annular upper surface, and the second segment protrusion extends around the entire second segment annular lower surface or the second segment depression extends around the entire second segment annular lower surface.
 4. The segmented silicon carbide liner of claim 1, wherein the bonding material comprises 0.4-0.7 wt % lithium as lithium aluminum silicate and silicon carbide.
 5. The segmented silicon carbide liner of claim 1, wherein at least one of the first silicon carbide segment and the second silicon carbide segment is constructed of reaction-bonded silicon carbide.
 6. The segmented silicon carbide liner of claim 5, wherein: the at least one of the silicon carbide segments has an inwardly facing surface; and the reaction-bonded silicon carbide has a surface contamination level, on the inwardly facing surface of the silicon carbide segment, of less than 1% atomic of phosphorus and less than 1% atomic of boron.
 7. The segmented silicon carbide liner of claim 1, wherein the second silicon carbide segment has an upper edge surface that defines an upwardly opening second segment depression.
 8. The segmented silicon carbide liner of claim 7, wherein the first segment upper edge surface defines an upwardly opening first segment depression and the second segment lower edge surface defines a downwardly extending second segment protrusion, the liner further comprising: one or more additional silicon carbide segments, each additional silicon carbide segment comprising an additional segment upper edge surface defining an upwardly opening additional segment depression and an additional segment lower edge surface defining a downwardly extending additional segment protrusion, the additional segment protrusion received within an upper edge surface depression of an adjacent silicon carbide segment located below and abutted to the additional silicon carbide segment and having smaller dimensions than the depression of the adjacent silicon carbide segment such that the surface of the adjacent silicon carbide segment depression is spaced apart from the surface of the additional segment protrusion and a space is located between the additional segment protrusion and the depression of the adjacent silicon carbide segment; and a volume of bonding material comprising a lithium salt, the bonding material disposed within the space between the additional segment protrusion and the depression of the adjacent silicon carbide segment.
 9. The segmented silicon carbide liner of claim 7, wherein the first segment upper edge surface defines an upwardly opening first segment depression and the second segment lower edge surface defines a downwardly extending second segment protrusion, the liner further comprising: a terminal silicon carbide segment located above and abutted to the second silicon carbide segment, the terminal silicon carbide segment having a terminal segment lower edge surface defining a downwardly extending terminal segment protrusion received within the second segment depression and having smaller dimensions than the second segment depression such that the surface of the second segment depression is spaced apart from the surface of the terminal segment protrusion and a space is located between the terminal segment protrusion and the second segment depression; and a volume of bonding material comprising a lithium salt, the bonding material disposed within the space between the terminal segment protrusion and the second segment depression.
 10. A fluidized bed reactor for production of polysilicon-coated granulate material, comprising: a vessel having an outer wall; and a segmented silicon carbide liner according to claim 1, the liner being positioned inwardly of the outer wall such that the inner surfaces of the liner segments define a portion of a reaction chamber.
 11. The fluidized bed reactor of claim 10, further comprising: at least one heater positioned between the outer wall and the segmented silicon carbide liner; at least one inlet having an opening positioned to admit a primary gas comprising a silicon-bearing gas into the reaction chamber; a plurality of fluidization gas inlets, wherein each fluidization gas inlet has an outlet opening into the reaction chamber; and at least one outlet for removing silicon-coated product particles from the vessel.
 12. A process for assembling a segmented silicon carbide liner for a fluidized bed reactor for production of polysilicon-coated granulate material, comprising: providing a first silicon carbide segment having a first segment upper edge surface defining an upwardly opening first segment depression; providing a second silicon carbide segment having a second segment lower edge surface defining a downwardly extending second segment protrusion configured to fit within the first segment depression, the second segment protrusion having smaller dimensions than the first segment depression to provide a space between the second segment protrusion and the first segment depression when the second segment lower edge surface is brought into contact with the first segment upper edge surface and the second segment protrusion is received within the first segment depression; applying a volume of bonding material comprising a lithium salt to at least one of a portion of the first segment depression or a portion of the second segment protrusion; bringing at least a portion of the lower edge surface of the second silicon carbide segment into abutment with the upper edge surface of the first silicon carbide segment with the bonding material therebetween; and applying heat to the bonding material, in an inert atmosphere, to form bonded first and second silicon carbide segments.
 13. The process of claim 12, further comprising applying the bonding material to the other of a portion of the first segment depression or a portion of the second segment protrusion before bringing the lower edge surface of the second silicon carbide segment into abutment with the upper edge surface of the first silicon carbide segment and before applying heat.
 14. The process of claim 12, wherein, prior to heating, the bonding material is an aqueous slurry comprising water, lithium silicate and silicon carbide particles.
 15. The process of claim 12, wherein applying heat comprises: exposing the abutted first and second silicon carbide segments to an atmosphere at a first temperature T1 for a first period of time; increasing the temperature to a temperature T2; and exposing the abutted first and second silicon carbide segments to the second temperature T2, wherein T2>T1, for a second period of time to cure the bonding material.
 16. The process of claim 15, wherein: the first temperature T1 is 90-100° C. and the first period of time is at least two hours; and the second temperature T2 is 250-300° C. and the second period of time is at least two hours.
 17. The process of claim 12, further comprising drying the abutted first and second silicon carbide segments for an initial period of time at ambient temperature before applying heat.
 18. The process of claim 17, further comprising exposing the abutted first and second silicon carbide segments to sunlight while drying at the ambient temperature. 